Scavenging singlet oxygen – A key to avoid photoinhibition
Light drives most life on earth as photosynthetic organisms convert it to a chemical energy. However, too much light causes photodamage that may lead to photoinhibition (PI). Photodamage happens when photosynthetic electrons/energy are being transferred from the excited chlorophyll molecule to oxygen. Those excited oxygen molecules are called ROS and they tend to damage the photosynthetic complexes and particularly the D1 of photosystem II. Living in the desert, the microalgae Chlorella ohadii is exhibiting exceptional resistance to extreme high light intensity. Here, we analyzed the ROS formation in C. ohadi grown at high light intensity where other photosynthetic organisms cannot survive. Examining the formation of different ROS revealed that singlet oxygen was almost completely depleted in HL cells compared to low light (LL) grown cells. These results implied that when grown in HL, a condition where massive amounts of protective carotenoids accumulate in the thylakoids, singlet oxygen formation is significantly reduced. Together with additional PI protection mechanisms that evolved in C. ohadii (Levin et al Plant J. 2021) the enormous quenching of ROS accumulation enables this alga to thrive at light intensities where others cannot survive.
